Import ESP_UniClock (upstream 1189810)

Vendored from https://github.com/gpeter62/ESP_UniClock: the sketch
source, the web UI and the libraries the ESP8266 build needs, unpacked
from the bundled zips. Adds a PlatformIO project for the ESP-12. The
source is unchanged; local changes follow as separate commits.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

firmware/uniclock/lib/ArduinoJson/extras/tests/JsonVariant/overflow.cpp

@@ -0,0 +1,72 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2022, Benoit BLANCHON
+// MIT License
+
+#include <ArduinoJson.h>
+#include <catch.hpp>
+
+template <typename TOut, typename TIn>
+void shouldBeOk(TIn value) {
+  StaticJsonDocument<1> doc;
+  JsonVariant var = doc.to<JsonVariant>();
+  var.set(value);
+  REQUIRE(var.as<TOut>() == TOut(value));
+}
+
+template <typename TOut, typename TIn>
+void shouldOverflow(TIn value) {
+  StaticJsonDocument<1> doc;
+  JsonVariant var = doc.to<JsonVariant>();
+  var.set(value);
+  REQUIRE(var.as<TOut>() == 0);
+  REQUIRE(var.is<TOut>() == false);
+}
+
+TEST_CASE("Handle integer overflow in stored integer") {
+  SECTION("int8_t") {
+    // ok
+    shouldBeOk<int8_t>(-128);
+    shouldBeOk<int8_t>(42.0);
+    shouldBeOk<int8_t>(127);
+
+    // too low
+    shouldOverflow<int8_t>(-128.1);
+    shouldOverflow<int8_t>(-129);
+
+    // too high
+    shouldOverflow<int8_t>(128);
+    shouldOverflow<int8_t>(127.1);
+  }
+
+  SECTION("int16_t") {
+    // ok
+    shouldBeOk<int16_t>(-32768);
+    shouldBeOk<int16_t>(-32767.9);
+    shouldBeOk<int16_t>(32766.9);
+    shouldBeOk<int16_t>(32767);
+
+    // too low
+    shouldOverflow<int16_t>(-32768.1);
+    shouldOverflow<int16_t>(-32769);
+
+    // too high
+    shouldOverflow<int16_t>(32767.1);
+    shouldOverflow<int16_t>(32768);
+  }
+
+  SECTION("uint8_t") {
+    // ok
+    shouldBeOk<uint8_t>(1);
+    shouldBeOk<uint8_t>(42.0);
+    shouldBeOk<uint8_t>(255);
+
+    // too low
+    shouldOverflow<uint8_t>(-1);
+    shouldOverflow<uint8_t>(-0.1);
+
+    // to high
+    shouldOverflow<uint8_t>(255.1);
+    shouldOverflow<uint8_t>(256);
+    shouldOverflow<uint8_t>(257);
+  }
+}